Chapter 16. UART Modules
16-25
Operation
16.5.2.2 Receiver
The receiver is enabled through its UCRn, as described in Section 16.3.5, “UART
Command Registers (UCRn).” Figure 16-26 shows receiver functional timing.
Figure 16-26. Receiver Timing
When the receiver detects a high-to-low (mark-to-space) transition of the start bit on RxD,
the state of RxD is sampled each 16
×
clock for eight clocks, starting one-half clock after
the transition (asynchronous operation) or at the next rising edge of the bit time clock
(synchronous operation). If RxD is sampled high, the start bit is invalid and the search for
the valid start bit begins again.
If RxD is still low, a valid start bit is assumed and the receiver continues sampling the input
at one-bit time intervals, at the theoretical center of the bit, until the proper number of data
bits and parity, if any, is assembled and one stop bit is detected. Data on the RxD input is
sampled on the rising edge of the programmed clock source. The lsb is received first. The
data is then transferred to a receiver holding register and USRn[RxRDY] is set. If the
character is less than eight bits, the most significant unused bits in the receiver holding
register are cleared.
After the stop bit is detected, the receiver immediately looks for the next start bit. However,
if a non-zero character is received without a stop bit (framing error) and RxD remains low
for one-half of the bit period after the stop bit is sampled, the receiver operates as if a new
start bit were detected. Parity error, framing error, overrun error, and received break
conditions set the respective PE, FE, OE, RB error, and break flags in the USRn at the
received character boundary and are valid only if USRn[RxRDY] is set.
C1
C2
C25
C27
C28
C29
C3
C26
C26, C27, and C82 are lost
(C2)
Status
Data
(C3)
Status
Data
(C4)
Status
Data
C26
is lost
Reset by
command
RxD
Receiver
Enabled
USRn[RxRDY]
Overrun
RTS
4
internal
module
select
USRn[FFULL]
(C1)
Status
Data
USRn[OE]
Automatically asserted
when ready to receive
Manually asserted first time,
automatically negated if overrun occurs
UOP0[RTS] = 1
Summary of Contents for DigitalDNA ColdFire MCF5272
Page 1: ...MCF5272UM D Rev 0 02 2001 MCF5272 ColdFire Integrated Microprocessor User s Manual ...
Page 38: ...xxxviii MCF5272 User s Manual TABLES Table Number Title Page Number ...
Page 58: ...1 10 MCF5272 User s Manual MCF5272 Specific Features ...
Page 90: ...2 42 MCF5272 User s Manual Exception Processing Overview ...
Page 96: ...3 6 MCF5272 User s Manual MAC Instruction Execution Timings ...
Page 158: ...5 46 MCF5272 User s Manual Motorola Recommended BDM Pinout ...
Page 184: ...7 12 MCF5272 User s Manual Interrupt Controller Registers ...
Page 338: ...13 44 MCF5272 User s Manual Application Examples ...
Page 414: ...18 6 MCF5272 User s Manual PWM Programming Model ...
Page 452: ...19 38 MCF5272 User s Manual Power Supply Pins ...
Page 482: ...20 30 MCF5272 User s Manual Reset Operation ...
Page 492: ...21 10 MCF5272 User s Manual Non IEEE 1149 1 Operation ...